# null byte
$data =~ s/\x00//g;

$data =~ s/"/"/g;
$data =~ s/\|/\|/g;

# to prevent sql injection
$data =~ s/drop/dr0p/ig;
$data =~ s/insert/ins3rt/ig;
$data =~ s/select/se1ect/ig; # letter 'l' becomes number '1'
$data =~ s/delete/de1ete/ig;
$data =~ s/alter/a1ter/ig;
$data =~ s/update/upd4te/ig;

# unix command?
$data =~ s/rrm//ig;

# javascript
$data =~ s/script/skript/ig;